The present invention relates to a mass spectrometer and a method of mass spectrometry.
A known mass spectrometer comprises an Electron Impact (“EI”) ion source in combination with a reflectron Time of Flight mass analyser. The known reflectron Time of Flight mass analyser comprises a series of ring electrodes which are connected to a potential divider or resistor chain. A RF voltage and a static DC voltage are applied across the ends of the potential divider or resistor chain so that a static axial DC voltage gradient and an inhomogenous axial RF voltage are maintained along the length of the mass analyser. The mass spectrometer further comprises an electron multiplier ion detector which is arranged in line with the central axis of the mass analyser at the position of zero field. At a predetermined phase of the RF voltage applied to the ring electrodes, ions formed by the Electron Impact ion source are pulsed into the Time of Flight mass analyser by applying a voltage pulse to an acceleration grid which is arranged adjacent to an entrance aperture of the mass analyser. Ions which are accelerated into the Time of Flight mass analyser travel a proportion of the length of the mass analyser before being reflected back towards the entrance of the mass analyser. The ions then exit the mass analyser, pass through the acceleration grid and are subsequently detected by the ion detector. The time of flight of the ions from the time that the voltage pulse is applied to the acceleration grid to the subsequent detection of the ions by the ion detector is related to the mass to charge ratio of the ions and the field parameters within the Time of Flight mass analyser.
One problem with the known Time of Flight mass analyser is that ions are not effectively confined radially within the mass analyser. Therefore, the ion transmission efficiency is relatively low.
Another problem with the known Time of Flight mass analyser is that the ions entering the mass analyser have a relatively large spread of initial velocities and initial positions which results in the resolution of the known Time of Flight mass analyser being relatively poor.
A further problem with the known Time of Flight mass analyser is that the mass analyser is only arranged to operate with an Electron Impact ion source which operates at a low pressure and hence the mass analyser is not arranged to operate with an atmospheric pressure ionisation ion source.
It is therefore desired to provide an improved mass spectrometer and method of mass spectrometry.